And uninstall whatever apps you really aren't using. Hard to know if one is the culprit without knowing what's on your phone, but it's always a good idea to clean house.
As a guide, I use the 60 day rule. If I haven't touched it in 60 days it's probably not that important and if I find that it was, I can always reinstall it.

Thanks for the really good response Harold. I will answer a little now but I have been driving all day to a trade show we are displaying at so I may add more tomorrow.

1 About 2 months ago. Nothing happened that should have triggered it.

2. It is a Samsung S6. I am not sure what version of Android. Tomorrow when I am not so tired I may see if I can find that someplace.

3. AT&T and yes

4. I have never added any security and I think it updated on it's own a few months ago and that could be when it started but I am not sure.

5. Yes, and I have not downloaded many apps myself. The only ones I have downloaded are Gas Buddy, Waze, TD Ameritrade and DJI for my Drone There are a ton of apps on the phone but I worry about deleting something that I don't know what it is since it may be something essential. Any other apps came with the phone.

6. Mostly ads but there may be one that shows weather or something like that. The last ad I noticed was for a pest control service. I don't pay much attention to them in the past and mostly just looked for how to get them to close.

7. No

8. It happens when I first take my phone out of sleep mode. Even if I am trying to answer an incoming call. Something I just noticed is that I am 400 miles from home right now and at least at the moment it isn't happening. That doesn't make sense to me but just thought I would mention it. The most distracting part is when I get an incoming call and have to close out three ad windows to get to where I can take the call.

9. I don't think it is the Chrome browser but it is whatever came on the phone. I will try and check that out.

10. No problems starting the phone or shutting it down and the only problem with calls is what I mentioned before.

That was a really helpful answer and I will play with some of those suggestions such as deleting any apps I don't use. I may google the app first and see what I am deleting just to be safe and will try the anti-virus. Thanks

6. Mostly ads but there may be one that shows weather or something like that. The last ad I noticed was for a pest control service. I don't pay much attention to them in the past and mostly just looked for how to get them to close.

Most free apps make money with ads. Check to see what weather app you have installed. I've never heard of ads happening outside of an app but these days nothing surprises me. If, for instance, you have a widget on your home screen from an app, that would technically be an app that is running all the time.

An S6 is a little long in the tooth, but Android and Samsung still push security updates.

As for uninstalling apps, it likely came with some bloatware by default. That's just what carriers do to us now. I'm sure there's an ATT app and some other partner crap.
Also phone deals purchased on Amazon come with ads on them, although that doesn't sound like the case.

Just go through and identify that ones you definitely know and use from companies you trust. The ones that you aren't sure what they do, or where they came from..those are your targets. Gotta identify what they are for and if you need them. Only way is to open them and see.

Some bloatware apps cannot be uninstalled ( I can rant about that crap later), but you can disable them. I can walk you through that if you think you've identified a culprit.
All in all, it sounds like a really aggressive app, like a weather app, or you have picked up some kind of malware somewhere.

Try that Avast scan. I used it for years and thought it was very good at identifying bad things.

If it's really bad and none of the above helps, you can always factory reset it. Factory reset will delete any files stored on the phone so you want to back those up, but by signing back into your Google account (and any other accounts that it's connected to), your contacts, settings and apps should restore.